This invention relates to a dispensing gun, and more particularly to a gun to be used with systems in which two or more fluid components that are separately stored in pressurized vessels are mixed and dispensed from the gun as a settable foam.
Manually operable guns are known for dispensing a settable urethane foam. Separate fluid components are fed individually to the gun, passed separately through control valves, and brought into contact with each other upon reaching a mixing chamber of a nozzle from which the mixed components are discharged as foam. Examples of such guns are found in U.S. Pat. Nos. 4,311,254 and 4,399,930 issued to Gary Harding and in U.S. Pat. No. 4,762,253 issued to Steven Palmert.
The two fluid components are commonly referred to as the "A resin" and the "B resin". They usually consist of polymeric isocyanate and polyol amine, respectively. The components are supplied separately in two pressurized containers that are attached by hoses to inlets to the guns. When the two fluid components or resins are mixed, the mixture quickly sets up to form a rigid foam product which is substantially insoluble and extremely difficult to remove from surfaces with which it comes in contact. As a result, the nozzles for the guns in which the two components are first mixed are typically designed to be replaceable and disposable so as to avoid the necessity for cleaning the nozzles.
Because of the quick set-up of the mixture of the two components, it is also important to keep the components separate within the gun so that their only contact is in the mixing chamber of the disposable nozzle. The two components are usually under different pressures in the respective tanks. If the nozzle should plug and the valves of the gun are opened, the higher pressure fluid could contaminate the lower pressure fluid and cause set-up of the resins within the gun thereby rendering the gun useless.
One of the components, the "A resin", has a tendency to harden on exposure to air. Even if the valves of the gun are closed, it is possible for the "A resin" to harden internally of the gun if exposed to air. That problem has been addressed in the past by adding a solvent flushing port to the "A resin" side of the gun body as shown in U.S. Pat. No. 4,516,694 issued to Clifford J. Finn.